Multilayer structures have been utilized for many years. The concept of a multilayer is that the positive properties of two or more different materials are combined with the integrity of each material being essentially uncompromised. Although many of these multilayers can be hypothesized on the basis of laminating a material possessing certain strong properties with a material having strong properties in other areas, certain practical considerations inhibit successful implementation of this theory. The two materials are in intimate contact at their interface. The compatibility of the two resins at this interface is generally not known until actually contacted at the high temperatures necessary to obtain adherence of the two layers. Where incompatibility is significant--the two layers pull apart with little external stressing force--a tie layer that binds the two relatively incompatible layers is necessary. In general, polymers of significantly differing chemical structure are relatively incompatible and require a tie layer for many of the structure's applications.
It has now been discovered that certain polymers with significantly differing chemical structures can be adjacent to each other in a multilayer composition without the benefit of a tie layer. Although not necessary for many applications, a tie layer may be interposed between the two layers for certain applications.